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Re: COUNT(*) again (was Re: [HACKERS] Index/Function organized

From: Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Hannu Krosing <hannu(at)tm(dot)ee>,Christopher Browne <cbbrowne(at)libertyrms(dot)info>,pgsql-performance(at)postgresql(dot)org,"pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: COUNT(*) again (was Re: [HACKERS] Index/Function organized
Date: 2003-10-05 13:36:40
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-hackerspgsql-performance
Tom Lane wrote:
> Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us> writes:
> > Tom Lane wrote:
> >> I think that's not happening, conditionally or otherwise.  The atomicity
> >> problems alone are sufficient reason why not, even before you look at
> >> the performance issues.
> > What are the atomicity problems of adding a create/expire xid to the
> > index tuples?
> You can't update a tuple's status in just one place ... you have to
> update the copies in the indexes too.

But we don't update the tuple status for a commit, we just mark the xid
as committed.  We do have lazy status bits that prevent later lookups in
pg_clog, but we have those in the index already also.

What am I missing?

  Bruce Momjian                        |
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